Abstract
Biochar has been widely recognized as an effective and eco-friendly ameliorant for saline soils, but information about the mechanism of how biochar influences nitrification in salt-affected agroecosystem remains fragmented. An incubation experiment was performed on the salt-affected soil collected from a three-consecutive-year experiment at biochar application gradients of 7.5 t⋅ha−1, 15 t⋅ha−1 and 30⋅t ha−1 and under nitrogen (N) fertilization. Responses of the nitrification rate (NR), numbers of ammonia monooxygenase (amoA) gene copies, and community structures of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to biochar application were investigated. The results indicated that, under N fertilization, the NR and numbers of amoA-AOB and amoA-AOA gene copies negatively responded to biochar addition. Biochar application increased the community diversity of AOB but decreased that of AOA. Biochar addition and N fertilization shifted the AOB community from Nitrosospira-dominated to Nitrosospira and Nitrosomonas-dominated, and altered the AOA community from Nitrososphaera-dominated to Nitrososphaera and Nitrosopumilus-dominated. The relative abundance of Nitrosospira, Nitrosomonas and Nitrosopumilus decreased, and that of Nitrosovibrio and Nitrososphaera increased with biochar application rate. Soil SOC, pH and NO3−-N explained 87.1% of the variation in the AOB community, and 78.1% of the variation in the AOA community was explanatory by soil pH and SOC. The SOC and NO3−-N influenced NR through Nitrosovibrio, Nitrosomonas, Norank_c_environmental_samples_p_Crenarchaeota and amoA-AOB and amoA-AOA gene abundance. Therefore, biochar addition inhibited nitrification in salt-affected irrigation-silting soil by shifting the community structures of AOB and AOA and reducing the relative abundance of dominant functional ammonia-oxidizers, such as Nitrosospira, Nitrosomonas and Nitrosopumilus.
Highlights
Introduction iationsNitrogen is an indispensable nutrient element for sustaining ecosystem productivity and plays a pivotal role in closing crop yield gaps to meet ever-increasing food demands [1].In salt-affected areas worldwide, extensively distributed saline soils, which are promising reserve land resources for compensating for the shortfall in food requirements, exert adverse impacts on crop growth and nitrogen nutrient uptake and result in nitrogen loss and environmental problems such as greenhouse gas emissions and nonpoint source pollution [2]
The nitrification rate (NR) varied temporally during the autotrophic nitrification process (Supplementary Figure S1), and the variation in NR could be ascribed to the dynamics of community structure and function of ammonia-oxidizing microorganisms, bioavailability of substrate, and soil microhabitat traits [23]
Under N fertilization conditions, biochar addition inhibited the average nitrification rate and numbers of ammonia monooxygenase (amoA)-ammonia-oxidizing bacteria (AOB) and amoA-ammoniaoxidizing archaea (AOA) gene copies in moderately salinized irrigation-silting soil, and the inhibitory effect increased with the biochar application rate
Summary
Nitrogen is an indispensable nutrient element for sustaining ecosystem productivity and plays a pivotal role in closing crop yield gaps to meet ever-increasing food demands [1]. In salt-affected areas worldwide, extensively distributed saline soils, which are promising reserve land resources for compensating for the shortfall in food requirements, exert adverse impacts on crop growth and nitrogen nutrient uptake and result in nitrogen loss and environmental problems such as greenhouse gas emissions and nonpoint source pollution [2]. The migration and transformation processes of nitrogen in agricultural ecosystems are greatly affected by soil salinity and derivative obstacle factors [3]. The amendment of soil salinization hazards is indispensable for enhancing soil productivity, improving nitrogen nutrient utilization, and minimizing environmental losses of nitrogen [4].
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